A variety of different earthmoving machines may be employed to move earth, rocks, and other materials from an excavation site. Often, it may be desirable to transport excavated material for a distance (e.g., haul distance) from an excavation site to another location (e.g., dump site) remote from the excavation site. Depending on the haul distance between the excavation site and the dump site, different types of earthmoving machines or techniques may be preferred over others. For longer haul distances (e.g., longer than a threshold haul distance), an off-highway haulage unit may be used to load earth, rocks, and other materials, and transport the loaded materials to the dump site. For shorter haul distances (e.g., shorter than a threshold haul distance), a tractor scraper may be used for excavating, hauling and dumping the excavated material.
Tractor scrapers may be preferred over other earthmoving machines for a number of reasons. In particular, tractor scrapers are versatile and may be employed in various industries, such as in agricultural, construction, mining, and other industries. Additionally, for relatively shorter haul distances, such as haul distances of approximately one mile or less, the design of tractor scrapers as well as the control schemes for tractor scrapers help to reduce operating costs, minimize operator skill and time, and improve overall efficiency and productivity. For instance, tractor scrapers may operate in substantially reiterative work cycles, where each work cycle may include cutting material from one location during a load segment, transporting the cut material to another location during a haul segment, unloading the cut material during a dump segment, and returning to an excavation site during a return segment to repeat the work cycle.
A conventional tractor scraper typically includes a tractor, a scraper attached to the rear of the tractor via an articulated joint. The tractor may support an operator cabin, a set of tractor wheels, and a combustion engine for driving the tractor wheels. The scraper may support a set of trailing scraper wheels, a bowl system and one or more work tools, such as elevators, conveyors, augers, spades, or the like, to aid in the loading or unloading of material. Once at the excavation site, the bowl system is lowered as the tractor scraper travels forward to cut or collect material from the ground. Once loaded, the bowl system is raised to provide sufficient clearance while hauling the loaded material to the dump site. At the dump site, the bowl system is lowered to dump the loaded material. Once fully unloaded, the bowl system is then raised again to provide the necessary clearance while traveling back to the excavation site.
Among other things, there is an ongoing interest to improve the overall performance and efficiency of tractor scrapers. For instance, one proposed improvement involves adding a separate engine to the rear scraper to help drive the rear wheels and to further enhance the productivity and flexibility of the tractor scraper. However, this configuration requires a rear transmission with speed ratios that typically differ from those of the front transmission, which further requires inefficient converter drives to ensure that rear wheel speeds match front wheel speeds. Operating a tractor scraper with two engines is also complicated by the need to operate two separate throttle pedals, one for each engine. Furthermore, conventional dual-engine tractor scrapers consume more fuel, without providing any adequate means for recovering and/or regenerating the energy expended.
One solution for overcoming the need for two engines while providing access to regenerative energy is to implement a power-split system. A power-split system can mechanically split the power output by a single engine to drive electric motors capable of both motoring and generating modes of operation. However, the application of power-split systems on tractor scrapers are precluded by the articulated nature of the joint between the front tractor and the rear scraper, and the typical levels of physical stress that are exerted on the articulated joint during normal operation. Implementing rigid structures to split or transfer the mechanical power output by the engine at the front of the tractor scraper to the rear wheels at the scraper over an articulated joint would not be cost-effective or feasible. Hydraulic-based regenerative solutions are also not feasible due to similar challenges associated with extending large diameter hydraulic piping across the articulated joint.
Yet another solution for improving the performance and efficiency of tractor scrapers without relying on dual-engines may be to employ electrical means of transferring power between the front tractor and the rear scraper. One such solution is disclosed in U.S. Pat. No. 4,207,691 (“Hyler”). In Hyler, an engine is provided in the rear scraper which drives the rear wheels and a generator. The electrical energy supplied by the generator is then applied to an electric motor in the front tractor to drive the front wheels. Similar to the dual-engine configuration, however, the configuration in Hyler still relies on a torque converter, a transfer shaft, and a transmission to adjust the speeds between the driven wheels. Furthermore, like in other conventional tractor scrapers, Hyler does not provide any means for recapturing or regenerating expended energy.
In view of the foregoing disadvantages associated with conventional tractor scrapers, a need therefore exists for more efficient, cost-effective solutions that not only facilitate operator control, but also improve overall performance thereof. Accordingly, the present disclosure is directed at addressing one or more of the deficiencies and disadvantages set forth above. However, it should be appreciated that the solution, provided by the present disclosure, of any particular problem is not a limitation on the scope of the present disclosure or of the attached claims except to the extent expressly noted.